Completionists

Player Overview, Statistics

DestinyStatus: Offers overall statistics (Xbox Live accounts only?). At-a-glance information on characters including faction progress, experience, and weekliesDestinyTracker: Offers more detailed statisticsGuardian.gg: If you’re looking for a Destiny player’s match history or elo, this one is great

Quality of Life

Destiny Item Manager (Chrome Web Store): A Google Chrome extension that is widely-regarded as being the best of its kind. Offers tools for min-maxing armor, filters
Ishtar Commander (Android, iOS): A mobile app
Loadouts for Destiny (iOS): A mobile app that allows for the creation and transfer of loadouts. More information at loadoutsapp.com